Abu Awad, a stalwart fighter for Islamic State, was unsettled. His battered men, sheltering in the rubble of bombed-out buildings, were running low on supplies and they were losing patience – and discipline.

“Abu Osama,” he said on a radio frequency that his pursuers were monitoring two streets away, from the other side of the frontline of the battle for Raqqa. “We don’t have water for ablutions, and we don’t have enough medicine to treat our injured.”

“Cleanse yourself with dirt and I will get some to you in the morning,” a man replied in a tired voice.

Fighters on the frontline in east Raqqa. Photograph: Achilleas Zavallis

A young Kurdish rebel was listening on a handheld radio and recognised the voice. “He’s Syrian,” he said, as others from his unit crouched around in the courtyard of a commandeered home. “That’s their leader, Abu Osama. One time [Isis] told us [on the same frequency]: ‘We will burn you, then bury you.’ There was no point replying.”

Around 300 Isis fighters are all that are thought to be left in the city, clinging to a corner of the capital of their so-called caliphate, which five months of relentless battle has reduced to three annihilated neighbourhoods. The Old City mud wall that had stood for more than a millennium flanks one side of the battleground, and a wasteland that was once an industrial area is on the other. Smoke from burning buildings mixed with raised grey dust from airstrikes shrouds both under an already dull autumn sky.

Burnt-out cars used as a temporary road blockade near a Syrian Democratic Forces base near the frontline. Photograph: Achilleas Zavallis

The extremists who have stayed have nowhere to go. Their fate is almost certain to be sealed in the apocalyptic ruins of the city where it all began for Isis in Syria more than four years ago.

What remains of the fight for Raqqa is now concentrated on a maze of ruined streets and homes that lead towards Clock Tower Square, where severed heads were placed on stakes after executions by Isis that residents were summoned to witness. Since 2013 the simple ringed roundabout has been scorched into the global psyche as an emblem of Isis’s menace. In the eyes of many, its looming loss will seal the terror group’s demise.

Bricks and twisted metal cover two empty boulevards leading to the square. Isis snipers line either side. Capturing it will symbolically destroy the group’s hold on territory it conquered and has been steadily losing for the past year. Through a hole in a wall used by a Kurdish sniper team, the square and its towering clock can be seen just under 500 metres away.

Destroyed buildings are seen through a sniper position overlooking Isis-held areas. Photograph: Achilleas Zavallis

While Isis used the Great Mosque of al-Nuri in Mosul to lay claim to be a group inspired by faith, Clock Tower Square showcased its naked savagery and intimidation. “There were around 13 executions a month,” said a local pharmacist, Ismael, who fled the city six months ago and joined a US-backed coalition known as the Syrian Democratic Forces (SDF). “They used to line the roundabout wearing masks, and go around the streets with a loudspeaker ordering people to watch.

“If you were a spy they cut your throat from the front. The same if you were a blasphemer or murderer. Magicians were beheaded from the back. Women were always shot.”

Fighters all along the frontline, men and boys – many of them also Raqqa locals – spoke matter-of-factly about events that would have been unfathomable before the Isis reign. “They came to get my brother from our home,” said Moussa, 21, pointing at the ruins of a home down the road. “They cut his head and hung his body on a crucifix near Aleppo. We weren’t even allowed to ask why.” Rami, another Arab fighter from Raqqa, also lost a brother to Isis members who came to his home. “They were Syrian, from among us, or else they wouldn’t have worn masks,” he said. “They also killed my mother at a checkpoint.”

Dalil, left, from Batman in Turkey, and Hazam, from Kobani, in their base in Raqqa. Photograph: Achilleas Zavallis

The men had based themselves in a grey three-storey building less than two miles south of the clock tower. The rooms festered with rotting food and flies. A toppled semi trailer blocked one entrance to the base, and sand berms closed off another. On the second floor, Hazam, 28, a Kurd from Kobani, incessantly barked instructions into a radio that he held in his only hand. His left hand was lost to a mortar in the fight for his home town two years ago, and when he pointed the stub of his wrist to direct his men, it seemed to have extra effect.

Just past a graveyard, in which Isis had shattered every tombstone, six young fighters had been sent the night before to flank the jihadists, but their position had been exposed. Two had been hit by an RPG, and the rest of the unit had been sent to rescue them. Hazam paced across a balcony as airstrikes thumped into Isis positions ahead. The blast wave shot past the brown mud walls of the Old City and into the headquarters. Shortly afterwards, his radio sparked to life. “Send the Hummer. We have two martyrs,” a man shouted. “And injuries. Four of them.”

An hour later, the US-supplied armoured jeep – the only one the unit had – roared up the street, the legs of the dead dangling out the back, the wounded crammed up front. A utility truck backed towards the Hummer and the two bodies were lifted on blankets and gently transferred to the open canopy. The wounded climbed in beside them. Dazed and deafened, one wounded boy rested his head on a corpse as the truck set off for a medical clinic, past an overturned lorry and jagged, abandoned homes.

An injured SDF fighter rests in the back of a truck on the way to hospital. Photograph: Achilleas Zavallis

Not a single civilian was left in east Raqqa. In their absence, graffiti sprayed on ruins spoke for them, as well as for the vanquished occupiers – and international groups who had come to fight. “The difference between men and apostates is prayer,” said one message scrawled by an Isis member. “Raqqa will be purified from the filth of the terrorists,” said another. Greek anarchists fighting alongside the Kurds and Arabs had also left their mark: “Rouvikonas, Raqqa 2017”, they had written, on a wall near the battle zone.

On both sides of the front, men and women from around the world have lined up to fight. Members of global leftist groups – Americans, Turks, Germans and Spanish, among others – flesh out the ranks of Kurdish and Arab fighters. And within the SDF, minorities from around the region have taken prominent positions.

At a medical centre, two Yazidi girls from Iraq – in their late teens, but looking much older – hosed and swept a courtyard where the two dead fighters had been brought a few hours earlier. Their four wounded colleagues squatted nearby. “I swear we didn’t even see them,” said one wide-eyed boy from Raqqa with a bandaged head. His colleague clasped his hands over his damaged ears.

The clinic’s doctor, Akif, a Kurd from the Turkish mountains, sat down and quickly dismissed the boys’ injuries. “They are just clumsy lads who need vitamins,” he said. “They can go back and fight.”

Akif held rank at the clinic, as did Turkish Kurds in two other frontline areas – where Hazam was based, and further away from the front in the suburb of Raqqa Samra, where Hevda, a woman in her late 30s, led a small but sensitive base. She swept the floors, cooked meals, kept guard, and held court whenever she wanted. “When you want something and you know it is right, it will come to you with courage and conviction,” she said. Kurds and Arabs in the base deferred to her, as they did to Dalil, from the Turkish city of Batman, who sat alongside Hazam in the forward base.

“The problem with Turkey is that it’s an intersection of capitalism and totalitarianism,” he said. “They have played an unfortunate role in the region.” Using a pejorative for the Turkish leader, Recep Tayyip Erdoğan, he added: “The sultan’s time is ticking.”

Arab volunteers, many of them locals, are prominent on the frontlines and, though neither group will acknowledge it publicly, recruiting local men has fired the battle with a sense of personal vengeance.

Near the frontline, with an Isis radio in one hand and another device to talk with his own men in the other, Elyas, 25, from Hasaka, said the role of the Raqqa ranks had been instrumental in the gains so far, as had precision airstrikes by a US-led coalition. “[Isis] know we don’t torture them if we catch them. I don’t even hate them,” he said. “They are ignorant people. They have been brainwashed. If we treat them like they treat us, we become like them.”

Elyas led his men through a hole blown in a wall near the front, then more holes smashed into adjoining homes, through which both the extremists and their pursuers moved. A bicycle stood incongruously amid the wreckage of war in one room. Strewn clothes and Islamic books covered the floor in another, alongside more rotting food. On the rooftop, Arab fighters crouched behind a wall as a rocket from a fighter jet crunched into an Isis position. Smoke from the blast drifted over nearby grain silos and silhouetted the graveyard. “I love the feeling of battle,” Elyas said as the sky darkened. “It’s delicious.”

As Isis withdrew, it burrowed underground to avoid the jets above. Tunnels are found most days, and nearly all have been booby-trapped. “The amount of energy they have put into laying mines is incredible,” said Elyas in a building up ahead. “We lost a comrade in the courtyard here.”

SDF fighters help a shell-shocked comrade to his feet. Photograph: Achilleas Zavallis

The stench of death lingered where both a tunnel and an improvised bomb had been found. An Isis man had been discovered there the day before. His body was buried nearby.

As the terror group’s fighters tire, the men hunting them say the fall of Raqqa has galvanised them. Commanders believe the city will fall within four to six weeks, and there is increasingly nowhere left to hide for the diehard extremists in the rubble and tunnels of what was once the centre of their rule in Syria.

The overwhelming destruction of Raqqa speaks of a place that has been through more than just war. The shattered psyche of the city hangs heavily over the battlefield. “Everything is broken,” said Ahmed Issa, a 25-year-old student. “My parents will never come back here. And I won’t let my sisters come. We are haunted by bad spirits here. Something needs to cleanse us.”